An internal combustion engine operates best when combustion is balanced among its cylinders. However, a number of factors contribute to cylinder-to-cylinder combustion variations, such as mechanical construction of the engine, engine condition, and combustion controls. To compound the problem, each cylinder can be fueled differently and breathe differently from cycle to cycle.
To help reduce cylinder combustion variation, some engine designers have used fuel balancing valves in the fuel lines upstream of the cylinders' fuel injection valves. These valves are used to adjust the fuel delivery to a given cylinder. Conventionally, adjustments are made until the peak firing pressures of all cylinders are equal.